Methamphetamine abuse and related problems: Methamphetamine (MA) is a highly addictive psychomotor stimulant that is a unique drug of abuse for several reasons, not the least of which includes its user population. There has been a dramatic increase in methamphetamine use in the United States over the past 25 years, especially among women. A recent survey by the Substance Abuse and Mental Health Services Administration showed that males are more likely to use marijuana, cocaine and hallucinogens, while men and women use methamphetamine at equal rates. In addition women tend to initiate methamphetamine use earlier than men and prefer to use methamphetamine over other addictive drugs. The use of methamphetamine has been linked to cognitive defect, violence, risk-taking behaviors and criminal activity, even among female users. For example, women methamphetamine users are considered to be significantly more violent than men. While high on methamphetamine, both male and female methamphetamine users also report engaging in risky sexual behaviors (e.g., unprotected, with strangers, with multiple partners at once), decreased sexual inhibition, heightened sexual desire and arousal, and enhanced sexual pleasure, and they engage in prolonged sexual contact. These risky sexual behaviors contribute to the spread of HIV/AIDS, which has been a major public health concern for several decades.
Another particularly unique characteristic of methamphetamine use is the way in which the drug is self-administered by humans, which is typically in a “binge and crash” manner. While a clear definition of the binge use of methamphetamine is lacking in current scientific literature, according to self-reports by methamphetamine users, a binge can be described as taking methamphetamine for a long period of time “until you run out [of the drug] or just can't physically do it anymore”. A methamphetamine binge in humans can range from 3-22 days. Furthermore, it has been reported that a history of unrestricted access to methamphetamine leads to increases in methamphetamine taking in both humans and animals.
Cognitive deficits (memory problems, decreased cognitive flexibility)—Data from both humans and animals show that chronic methamphetamine use can lead to disruptions of brain functioning that can affect both behavioral and neurochemical functioning, including deleterious effects on memory and cognition. Additionally, chronic methamphetamine use has been established as a risk factor for neuropsychological impairment. Approximately 40% of individuals who chronically use methamphetamine exhibit neurocognitive impairments, resulting in problems with executive functioning and psychomotor skill functioning. Even more striking, more than two-thirds of methamphetamine-dependent users exhibit impairment in overall learning, free recall and repetitions. Of particular importance are the effects of methamphetamine on episodic memory. Episodic memory is unique since it is the memory of learning a particular event, as well as what was learned during the event. Nearly 50% of methamphetamine-dependent individuals demonstrate impaired episodic memory, making it the most common type of memory affected in methamphetamine users. This impairment in episodic memory is characterized by a limited use of higher-level encoding, decreases in cognitive flexibility and increases in perseverance. Brain regions involved in cognitive function and memory include the prefrontal cortex, hippocampus, striatum and amygdala. Although the precise mechanisms by which methamphetamine disrupts episodic memory are unknown, it is generally believed that these cognitive disruptions are due to the neurotoxic effects of methamphetamine on dopaminergic, serotonergic and noradrenergic neurons in these brain regions. For example, human and animal studies have shown that depletion of dopamine (DA) in the striatum can lead to deficits in overall reaction task performance. Additionally, disruptions in serotonin (5-HT) and dopamine signaling have been shown to increase impulsivity, while depletion of central serotonin can disrupt the ability to accurately detect and respond to visual stimuli, all of which impair the ability of a subject to complete a learning or memory task.
Aberrant sexual behavior (sexual deviance, risky sexual behavior, HIV transmission)—With continued use of methamphetamine, especially when the user progresses to intravenous administration, the drug becomes primarily associated with sexual activity. The association between methamphetamine use and sexual risk taking has been well documented in men and predominantly among men who have sex with men. Studies have shown that methamphetamine use in men has been associated with high-risk sexual behaviors such as having a higher number of sexual partners, infrequent condom use, trading drugs or money for sex, having sex with a partner who is an injection drug user, as well as reports of a recent sexually transmitted infection (STI). While fewer studies have been conducted to examine the relationship between methamphetamine use and the risk of STIs among women, there are data suggesting that the proportion of methamphetamine use by either sex is more similar than with other illicit substances. Interestingly, current literature reviews suggest higher rates of bacterial STIs reported in female as compared with male drug users. Women may be more susceptible to STIs owing to the increased likelihood of asymptomatic infection and the practice of exchanging sex for money or drugs. One study of injection drug users found that methamphetamine-injecting women were more likely to have unprotected vaginal sex and multiple sex partners compared to women who injected other substances. A recent review of sexual behaviors among heterosexual drug users indicated that women methamphetamine users were at increased risk for engaging in unsafe sexual behaviors. Other studies have documented that women experience a heightened sex drive and increased number of sexual acts under the influence of methamphetamine. Qualitative data also suggest that methamphetamine use increases sexual desire and pleasure and reduces inhibition, which can alter/increase sexual behaviors in women. Recent preclinical research in rodent models of drug-induced sexual motivation also revealed a critical role for progesterone signaling in the medial amygdala on methamphetamine-related sexual behaviors in female rats. However, despite existing evidence, there is an urgent need for further research on sexual-risk behavior among women who use methamphetamine because of their potentially high risk for STIs and HIV.
There is currently not a treatment available that reduces methamphetamine cravings and medical and behavioral consequences of methamphetamine use or the HIV associated cognitive motor disorders and HIV-associated neurodegenerative disorders.